Backing paper is used to separate uncured pre-impregnated material used to fabricate composite structures. The backing paper operates to maintain separation between layers of pre-impregnated material as it is rolled up so that the pre-impregnated material does not stick to itself during transportation and storage. The combined pre-impregnated material and backing paper roll may then be unrolled during fabrication by automated or manual means and the backing paper can be removed thrown away as the pre-impregnated material is applied to a second material to create a layered material. Such backing paper typically includes a coating material that enables the backing paper to be more easily removed from the uncured pre-impregnated material. A problem that may arise in the process is that a portion of the backing paper can sometimes remain attached to the pre-impregnated material and become sandwiched in the layered material. This produces FOD that creates a weak region or defect in the layered material. Such backing paper FOD can be very difficult to detect using typical non-destructive examination (NDE) methods, such as ultrasound testing, infrared thermography, or x-ray testing.
One reason that detection is difficult is because the backing paper may be of similar ultrasonic impedance as the layered material, and may not create as strong a reflection as an air void or delamination. Similarly, the backing paper may not create a strong thermal transport difference for infrared thermography to detect. If a section of backing paper remains on the uncured pre-impregnated material, traditional non-destructive examination may be even more likely to miss the backing paper since the area with the backing paper will appear uniformly good. Such backing paper remaining between layers of a layered material may cause failure of the component, if it is not detected. Therefore, an improved backing paper that is easier to detect under traditional non-destructive examination may be desirable.